PLATE XLVIl. 



(Figs. 1-6, 12, 16-M, •33-34 by E. Emmons; 7-11, 13-15, 21 by G. B. Simpson.) 



Legend: p. Pedicle-cavity. r. Diductots. 



vc. Visceral canal. v. Vascular sinuses. 



a. Adductors. ub. Umlional blades of primary lamelliE. 



a'. Anterior adductors. al. Accessory lamellse. 



Genus ATHYRIS, McCoy. 



Page St. 



Subgenus SEMINULA, McCoy. 

 Seminula Rogeksi, sp. uov. 



Fig. 1. A dorsal view of an internal cast of conjoined valves. 



Fig. 2. A ventral view of a similar specimen ; showing the cast of the pedicle-cavity and muscular scars. 

 Fig. 3. A cardinal view of the specimen represented in figure 2 ; showing, in addition to the features men- 

 tioned, the casts of the visceral foramen and hinge-plale. 

 Fig. 4. A profile of the specimen repi-esented in figure 1. 



Pendleton sandstone. Pendleton, Indiaiia. 



Seminula trinuclea, Hall. 



Fig. 5. A dorsal view of conjoined valves ; showing the contour of the species. X 2. 

 Fig. 6. A frontal view of the same specimen. X 2. 



St. Louis limestone. Blomnivgton, Indiana. 

 Fig. 10. A ventral view of an internal cast of conjoined valves; showing the filling of the pedicle-cavity 



and the small muscular scar. X li- 

 Fig. 11. A dorsal view of the same specimen ; showing the filling of the pedicle-cavity and the visceral 

 foramen, the cavity of the dental and hinge-plates, aud the faint muscular area. X 1^. 

 St. Louis group. Spergen Hill, Indiana. 

 Fig. 12. A dorsal view of a more strongly trilobed internal cast ; showing with greater distinctness the 

 character of the musculai' area. 



St. Louis group. Harrison county, Indiana. 

 Fig. 13. A view of the hinge-plate ; showing its subquadrate outline and the prolongation of the crural 



lobes. X 5. 

 Fig. 14. The same specimen viewed from the beak, the latter being removed to show the elevation of the 

 posterior extension of the plate, and exposing the visceral foramen. X 5. 

 St. Louis group. Spergen Hill, Indiana. 



Seminula subquadrata, Hall. 



Fig. 7. A dorsal view of conjoined valves, showing the sharp and distant concentric lines. 



Chester limestone. Crittenden county, Kentucky. 

 Fig. 8. A dorsal view of a somewhat more orbicular form. 

 Fig. 9. A profile of the same specimen. 



This shell is associated with typical forms of iS. trinuclea and at this locality passage forms 

 between these two extremes of expression are readily found. At other localities this form may 

 prevail to the exclusion of the others. 



St. Louis limestone. Spergen Hill, Indiana. 

 Fig. 15. The interior of a brachial valve of a more distinctly trilobed individual ; showing the adductor 



scars anil the hinge-plate which is slightly broken on the anterior mai-gin. 

 Fig. 16. An anterioi- view of the hinge jilate ; showing the visceral foramen and the elevation of the crural 

 plates and lobes. X 3. 



St. Louis limestone. Pella, Iowa. 



